Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-05-04
2001-10-02
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S130000, C342S357490
Reexamination Certificate
active
06298083
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to power management in a signal receiver. More particularly, the present invention relates to reducing power consumption in a Global Positioning System (GPS) receiver.
BACKGROUND OF THE INVENTION
Signal acquisition in a Global Positioning System (GPS) receiver generally requires searching for a modulation code in a carrier signal that is received from a GPS satellite. GPS generally makes use of two spread-spectrum modulation codes known as the “C/A code” and the “P code”, which are multiplexed in quadrature onto a single carrier. The C/A code is a Gold code with a chipping rate of 1.023 Mbits/sec and is used for making course position determinations. The P code is a pseudo-random code with a chipping rate of 10.23 Mbits/sec and is used for more precise position determinations. The P code is more resistant to jamming than the C/A code and has a secure, “antispoof” version known as the Y code. The Y code is available only to authorized users, such as the military. The P code and the Y code are sometimes referred to collectively as the P(Y) code.
Code acquisition in a GPS receiver may be accomplished by comparing the received code with a reference code generated locally within the receiver in order to synchronize the two codes. The time required to acquire the signal is generally dependent upon frequency and phase uncertainties between the received code and the reference code. Consequently, acquisition of the received code generally involves searching a two-dimensional search region defined by a number of code offset values in one dimension and a number of frequency offset values, sometimes referred to as Doppler offset values, in the other dimension. The code offsets represent different values of phase offset between the received code and the reference code, while the frequency offsets represent different values of frequency offset between the received code and carrier and the reference code and carrier. The code and frequency offset values which define the search region are sometimes referred to as “bins”.
Thus, referring to
FIG. 1
, the acquisition of a P(Y) code received from a GPS satellite is performed by searching for a signal
20
within a search region
21
. The search region
21
is defined in terms of a number of code offset bins along one axis and a number of frequency offset bins along a second axis. Element
22
in
FIG. 1
represents a bin. The signal acquisition time is the time from the start of the search until a bin is determined to be occupied or “hit”.
The process of synchronizing the locally-generated code to the received code in a GPS receiver often involves computing the correlation between the two codes at various points in time. Referring to
FIG. 2A
, two correlation curves
31
and
32
are associated with two adjacent code offset bins. In the direction of code offset, the shape of the correlation function may be a series of overlapping triangles, the peaks of which are centered at the midpoint of each code offset bin, and the troughs of which fall halfway between each bin. The width of each bin is the width of each triangle at the code offset axis. Although the bins overlap, the midpoints of the bins are spaced apart by C chips; hence, the bins are said to be spaced apart by C chips. The rate at which a search region may be covered generally depends upon the number of parallel search bins and the degree of overlap of adjacent bins. The most adverse condition in terms of signal correlation is for the received signal to be located exactly midway between the center points of adjacent bins. For example,
FIG. 2A
illustrates that signal correlation is strongest when the actual code offset corresponds to the center of a bin and weakest when the offset corresponds to the trough
33
between two bins. Signal acquisition time, therefore, depends partially upon the “depth” of the trough
33
. The depth of the trough
33
, in turn, is directly dependent upon the spacing of the bins. If the bins are spaced farther apart, the total number of bins to be searched within a given search region may be reduced; however, the overall acquisition time may increase due to the increased trough depth. These principles, therefore, give rise to a design trade-off between bin spacing and signal acquisition speed.
FIG. 2B
shows a relationship between frequency offset and signal correlation. In the direction of frequency offset, the shape of the correlation function is a series of overlapping sinc(x) curves, the peaks of which are centered at the midpoint of each frequency offset bin and the troughs of which fall halfway between each bin. Curves
34
and
35
represent the correlation curves associated with two adjacent frequency offset bins. The bins associated with curves
34
and
35
overlap but are spaced apart by F Hz. The width of the frequency offset bins is the width between the nulls of each sinc(x) curve at the frequency offset axis. As with code offset, the depth of the trough
36
depends partially upon the spacing of the bins.
A problem that is associated with many GPS receivers is power consumption. Random access memory (RAM) in the receiver can be a significant source of power consumption. A GPS receiver may include RAM for providing accumulators to store correlation data used during signal acquisition. Conventional dynamic RAM (DRAM) based on Complementary Metal-Oxide-Semiconductor (CMOS) process draws power each time it is accessed during a read or write cycle. Thus, it is desirable to reduce power consumption in a GPS receiver and, in particular, to reduce power consumption associated with RAM accumulators in a GPS receiver.
SUMMARY OF THE INVENTION
One aspect of the present invention is a method and apparatus for reducing power consumption in a receiver that includes multiple correlation segments that are operable in parallel. Each of the correlation segments has a separate set of storage locations associated with it. In each of the correlation segments, correlation data associated with multiple signals are generated. The correlation data are stored during each of multiple time intervals by accessing the storage locations of less than all of the correlation segments during each time interval.
In another aspect of the invention, correlation data generated in a given correlation segment are combined with correlation data generated in each other correlation segment to form data to be stored in the storage locations of the given correlation segment.
In particular embodiments, the multiple correlation segments may be cross-coupled, so that correlation data generated in any given correlation segment are added to correlation data generated in each other correlation segment, and the combined correlation data are stored in a set of accumulators for that correlation segment. The accumulators of only one correlation segment are accessed at a time to reduce power consumption in the receiver.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows.
REFERENCES:
patent: 4203070 (1980-05-01), Bowles et al.
patent: 4550414 (1985-10-01), Guinon et al.
patent: 5564098 (1996-10-01), Rodal et al.
patent: 5600670 (1997-02-01), Turney
patent: 5615236 (1997-03-01), Turney
patent: 6023489 (2000-02-01), Hatch
patent: 6028883 (2000-02-01), Tiemann et al.
patent: 6047017 (2000-04-01), Cahn et al.
patent: 6052405 (2000-04-01), Nakano
patent: 6064688 (2000-05-01), Yanagi
patent: 6118808 (2000-09-01), Tiemann et al.
Carlson Andrew B.
Crerie Jeffrey
Turney Paul
Westcott David C.
Blakely , Sokoloff, Taylor & Zafman LLP
Pham Chi
Tran Khai
Trimble Navigation Limited
LandOfFree
Power savings technique for a positioning system receiver does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power savings technique for a positioning system receiver, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power savings technique for a positioning system receiver will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2614958